The present invention generally relates to the use of gellable treatment fluids in subterranean operations, and, more specifically, to the use of gellable treatment fluids comprising derivatized hydroxyethylcellulose, hydrolysable in-situ acid generators, chelating agents, brines, and crosslinking agents, and methods of using these treatment fluids in subterranean operations.
Treatment fluids can be employed in a variety of subterranean operations. As used herein the terms “treatment,” “treating,” other grammatical equivalents thereof refer to any subterranean operation that uses a fluid in conjunction with performing a desired function and/or for achieving a desired purpose. The terms “treatment,” “treating,” and other grammatical equivalents thereof do not imply any particular action by the fluid or any component thereof. Illustrative subterranean operations that can be performed using treatment fluids can include, for example, drilling operations, fracturing operations, sand control operations, gravel packing operations, acidizing operations, conformance control operations, fluid diversion operations, fluid blocking operations, and the like.
In many cases, treatment fluids can be utilized in a gelled state when performing a treatment operation. For example, in a fracturing operation, a treatment fluid can be gelled to increase its viscosity and improve its ability to carry a proppant or other particulate material. In other cases, a gelled treatment fluid can be used to temporarily divert or block the flow of fluids within at least a portion of a subterranean formation. In the case of fracturing operations, the gelled treatment fluid typically spends only a very short amount of time downhole before the gel is broken and the treatment fluid is produced from the wellbore. In fluid diversion or blocking operations, the gel typically needs to remain in place only for a short amount of time while another treatment fluid is flowed elsewhere in the subterranean formation.
When conducting subterranean operations, it can sometimes become necessary to block the flow of fluids in the subterranean formation for a prolonged period of time, typically for at least about one day or more. In some cases, the period of time can be much longer, days or weeks. For example, it can sometimes be desirable to impede the flow of formation fluids for extended periods of time by introducing a kill pill or perforation pill into the subterranean formation to at least temporarily cease the communication between wellbore and reservoir. As used herein, the terms “kill pill” and “perforation pill” refer to a small amount of a treatment fluid introduced into a wellbore that blocks the ability of formation fluids to flow into the wellbore. In kill pill and perforation pill applications, high density brines can be particularly effective as a carrier fluid, since they can form a highly viscous gel that blocks the flow of fluids within the wellbore by exerting hydrostatic pressure therein. Likewise, in fluid loss applications, it can sometimes be desirable to form a barrier within the wellbore that persists for an extended period of time.
For subterranean operations requiring extended downhole residence times, many gelled treatment fluids can prove unsuitable since they can break before their intended downhole function is completed. The premature break of gelled treatment fluids can be particularly problematic in high temperature subterranean formations (e.g., formations having a temperature of about 275° F. or above), where the elevated formation temperature decreases the gel stability and speeds gel decomposition. As subterranean operations are being conducted in deeper wellbores having ever higher formation temperatures, the issues with long-term gel stability are becoming an increasingly encountered issue as existing gels are being pushed to their chemical and thermal stability limits.
Traditionally, the decomposition of a gel into lower viscosity fluids may be accomplished by using a breaker. An external breaker may be needed to remove a fluid loss pill upon well completion. Breaker compounds useful in high temperature formations may have high corrosion rates and may be harmful to the formation. Hydrochloric acid can be spotted on top of the gelled fluid. If HCl is spotted above the pill it takes time to break the pill as the acid must diffuse down through the pill and multiple spotting can be required depending on the gel-pill size, density of acid vs. the density of the pill and the well bore temperature. Additionally, operators usually prefer to use a self-degrading pill instead of a pill needing an external breaker. Therefore, a need exists for self-degrading, crosslinkable treatment fluid useful in subterranean operations.